Electric Field In Air Research Articles

On propagation of positive and negative streamers in air in uniform electric fields

Recently published results of numerical simulations of positive and negative streamers propagating in uniform applied electric fields in air are analyzed in the framework of an analytical approach. It is shown that obtained approximate relations between the streamer radius, velocity and length, depending on the value of applied electric field, are in reasonable agreement with the computational data.

Modeling Low‐Frequency Radio Emissions From Terrestrial Gamma Ray Flash Sources

AbstractRelativistic runaway electron avalanches (RREAs) occur when electrons in electric fields in air reach energies above which they gain more energy from the electric field than they lose to collisions with the surrounding atmosphere. RREAs are known to happen in the electric fields in thunderstorms, and are considered to be the mechanism responsible for producing Terrestrial Gamma‐ray Flashes (TGFs). As RREAs propagate, they leave a trail of low‐energy electrons and positive and negative ions behind. These populations of charged particles will carry currents as they move in the thunderstorm electric field. In the present work, we model the charged species left behind by the propagating RREA, and the resulting radio emissions in the context of injection of thermal runaway seed electrons by a leader. We find that for certain initial conditions, these radio emissions match the slow low‐frequency (LF) pulses that have previously been observed concurrently with TGFs. This confirms that the slow LF pulses are likely generated directly by the TGF source itself, as has been previously suggested using a different TGF production model. Slow LF pulses may therefore potentially be used to infer characteristic properties of TGF sources.

Experiments of forward THz emission from femtosecond laser created plasma with applied transverse electric field in air

The radiation from laser created plasma with applied electric field is studied numerically and experimentally. We experimentally observed short terahertz radiation with frequency of 0.2 THz forward direction in air using the THz time domain spectroscopy system. The two-dimensional particle in cell simulation shows that the radiation frequency is inversely proportional to the plasma diameter and is good agreement with experimental data.

Streamer Breakdown with Runaway Electrons Forming Diffuse Discharges in an Inhomogeneous Electric Field

The results of experimental investigations of formation of diffuse nanosecond discharges in a nonuniform electric field in air and other gases at the pressures within 12.5–400 kPa are presented. The experiments were performed using a four-channel ICCD-camera, an ultra-fast streak-camera, and wideband oscilloscopes. It is found out that spherical streamers are formed in a sharply nonuniform electrical fields under high voltages in a pre-breakdown stage of the discharge, irrespective of the gas used (air, nitrogen, hydrogen, methane, neon, or helium). The data are obtained on the instantaneous streamer velocity in air at different voltages and on the displacement current caused by the electric field re-distribution in the gap during the streamer formation. Beams of runaway electrons are recorded. The mechanism of formation of anode- and cathode-directed streamers at high voltages is discussed.

The Initial Stage of Diffuse Jet Formation in a Pulsed Discharge with a Non-Uniform Electric Field in Air

Laboratory simulation of the conditions for the occurrence of blue jets in the Earth’s atmosphere has been carried out. For this purpose, the diffuse formation of jets and plasma buildup in corona and apokampic discharges in air has been studied. It is shown that the jets are formed due to streamer breakdown and their color depends on air pressure. At atmospheric air pressures of 30–120 Torr, streamers starting from different parts of a repetitively pulsed discharge are recorded in a nonuniform electric field. It has been ascertained that a spherical corona discharge is formed before a breakdown between pointed electrodes, near a metal high-voltage electrode of positive polarity, from which streamer coronas start as the voltage increases. Data on the streamer head size and streamer propagation speed in the corona and apokampic discharges are presented.

Assessment of Surface Degradation of Silicone Rubber Caused by Partial Discharge

This paper reports experimental and analytical results of partial discharge degradation of silicone rubber sheets in accordance with proposed procedures. Considering the actual usage condition of silicone rubber as an insulating material of polymer insulators, an experimental procedure is established to evaluate long-term surface erosion caused only by partial discharge. Silicone rubber is subjected to partial discharge for 8 h using an electrode system with air gap. Voltage application is stopped for subsequent 16 h for recovery of hydrophobicity. The 24 h cycle is repeated 50 or 100 times. Deterioration of sample surface is evaluated in terms of contact angle and surface roughness. It is confirmed the proposed experimental procedure has advantage of no arc discharge occurrence, good repeatability of results, and possible acceleration of erosion. Surface erosion of silicone rubber progresses gradually and finally breakdown of silicone rubber occurs. Alumina trihydrate (ATH), an additive to avoid tracking and erosion by discharge, is not necessarily effective to prevent breakdown caused by partial discharge when localized electric field in air is enhanced by adding ATH. In such a situation, lower permittivity and higher resistance of silicone rubber seem dominant factors to prevent partial discharge breakdown and a careful insulation design should be required.

Electromagnetic scattering of charged particles in a strong wind-blown sand electric field**Project supported by the National Natural Science Foundation of China (Grant Nos. 11562017 and 11302111), the CAS “Light of West China” Program (Grant No. XAB2017AW03), adn the Major Innovation Projects for Building First-class Universities in China’s Western Region (Grant No. ZKZD2017006).

Some field experimental results have shown that the moving sands or dust aerosols in nature are usually electrified, and those charged particles also produce a strong electric field in air, which is named as wind-blown sand electric field. Some scholars have pointed out that the net charge on the particle significantly enhances its electromagnetic (EM) extinction properties, but up to now, there is no conclusive research on the effect of the environmental electric field. Based on the extended Mie theory, the effect of the electric field in a sandstorm on the EM attenuation properties of the charged larger dust particle is studied. The numerical results indicate that the environmental electric field also has a great influence on the particle’s optical properties, and the stronger the electric field, the bigger the effect. In addition, the charged angle, the charge density, and the particle radius all have a specific impact on the charged particle’s optical properties.

The initial stage of the diffuse jet formation in a pulsed discharge with a non-uniform electric field in air

The initial stage of the diffuse jet formation in a pulsed discharge with a non-uniform electric field in air

Ps four-wave mixing measurements of electric field in a ns pulse discharge in a hydrogen diffusion flame

Time-resolved electric field in ns pulse discharge plasmas generated in room air and in an atmospheric pressure hydrogen diffusion flame has been measured by ps four-wave mixing, for plane-to-plane electrode geometry. Electric field is put on the absolute scale using the Laplacian field measured before breakdown. The results show that peak electric field during breakdown in the flame, approximately 40 kV/cm, is significantly lower compared to that in room air, 75 kV/cm, due to higher temperature of combustion products. In both cases, peak electric field is higher compared to DC breakdown field. Both in air and in the flame, the electric field follows the applied voltage before breakdown and decreases rapidly after breakdown, due to charge separation and plasma self-shielding. The electric field in air is compared with the predictions of an analytic model of ns pulse breakdown, showing good agreement between the predicted and the measured breakdown field. The model also predicts earlier breakdown as well as breakdown voltage reduction as the temperature is increased, in qualitative agreement with the experimental data. The use of the present ps four-wave mixing diagnostics for measurements of electric fields below ∼20 kV/cm in atmospheric pressure flames is challenging, due to low signal-to-noise. The sensitivity of the present diagnostics is controlled by the high temperature and low N2 fraction in the combustion product mixture, as well as by the limited bandwidth of the Stokes beam generated by the stimulated Raman cell, which provides access only to several rotational levels of nitrogen molecules. The present diagnostics will have much better sensitivity in high-pressure flames, since the four-wave mixing signal scales as the squared number density of nitrogen.

Challenges when measuring the DC electric field very close to an insulator surface

A small probe that can measure DC electric fields in air has been developed. As a consequence of the probe size, it is possible to measure close to the surface of e.g. an HVDC insulator, and to resolve the field with an excellent spatial resolution. However, challenges have been identified when performing measurements close to a surface and its influence on the measurement results have been quantified. Measurement procedures have been developed to be able to correct for the possible net charging of the probe.

Experimental study on the movement of non-spherical particles in nonuniform electric field

The deactivation of free particles is an important issue for improving the insulating capability and reliability of high-voltage systems. In this work, we carry out experiments to investigate the electromechanical behavior of the non-spherical conducting particles for different particle orientations on either bare or coated electrode. Spheroidal and wire-shaped particles are used for the experiments. The particle motion is observed for two principal orientations with respect to the applied electric field in air. The results show that on a bare electrode, both kinds of particles exhibit the liftoff motion when the particle axis is aligned with electric field gradient. The field nonuniformity enhances the upward rotation of the particle tip subjected to the higher electric field. When the particle axis is parallel with a constant field line, the wire-shaped particle is more readily to make a rolling motion to the region of stronger electric field in comparison with the spheroidal particle, which shows higher occurrence rate of liftoff. The motion onset electric field decreases with increasing field nonuniformity. On the insulated electrode, the wire-shaped particle shows exclusively the rolling motion, whereas the spheroidal particle may make a rolling motion or rotate horizontally so as to align its axis with electric field gradient.

Effect of air breakdown in near-field region on maximum power radiated from aperture antenna

The high-power microwave easily causes the air breakdown in the near-field region of an antenna that is one of major factors to limit the enhancement of the radiation power at present. We study the maximum radiation power of a circular aperture antenna at which the maximum electric field in the near-field region equals the breakdown electric field in air, by using the field equivalent principle along with the global model. Results show that, with the pulse width increasing, the maximum radiation power decreases. The larger the antenna radius, the higher power can be radiated. The field distribution on the aperture has an obvious impact on the maximum radiation power.

Classification of impulse breakdown mechanisms under non-uniform electric field in air

To clarify the breakdown mechanism and the conditions leading to the breakdown under non-uniform electric field in air, we studied the details of breakdown characteristics and mechanism in air by using an ultra-high speed measurement system. We clarified that there were two types of breakdown mechanism in air. The one is the channel heating breakdown, and the other is the leader-type channel development breakdown. These breakdown mechanisms are dominated by three conditions: arrival of secondary streamer from high-voltage anode to opposite grounded cathode, channel heating, and leader-type channel initiation. We studied these conditions quantitatively, and revealed the conditions leading to the breakdown, and the breakdown mechanisms in air were classified. Finally, we clarified the factors, e.g. critical instantaneous power for the secondary streamer arrival, dominating these conditions based on the breakdown mechanism under non-uniform electric field in air.

Experimental Study on the Movement of Conducting Spheroidal Particles under Electric Field in Air

Study on the movement of conducting particle is useful for managing particles in gas insulation systems. The authors observed the movement of conducting prolate spheroidal particles under uniform electric field in air. From the experimental results we found three patterns of the movement. The critical electric field results in particle rotating or lifting. The particles rotated about the contact point before lifting in most cases. The measured particle-rotating field was lower than the analytical ones by 6 and 21% for 9 and 18 mm gaps, respectively. From the experiment, the size of the particles and the gap distance affect the critical field. The voltage polarity has no effect on the critical field for particle movement because of little difference between the experimental values of positive and negative polarities.

Modulated corona nanosecond discharge in air under ambient pressure

A unique type of corona discharge-modulated corona nanosecond discharge-has been obtained, the parameters of which have been determined in a geometric system of electrodes with a sharply heterogeneous electric field in air under ambient pressure and natural humidity.

Calculation of the Effective Ionization Rate in Air by Considering Electron Detachment From Negative Ions

The effective Townsend ionization coefficient in dry air at different pressures and temperatures is calculated by considering ionization by direct electron impact, attachment of electrons to molecular oxygen, simplified negative ion kinetics, and detachment of electrons from negative ions in collisions with heavy neutrals. Effect of electron detachment from negative ions created by primary and secondary electron avalanches propagating in a uniform electric field in air at different pressures and temperatures and its contribution into the effective ionization rate are analyzed.

Study of the Threshold Characteristics of a Discharge from Aerosol Particles

We study experimentally and theoretically the threshold of discharge ignition from conducting particles in a uniform electric field in air as a function of the particle size and shape. It is established that the threshold field increases with decreasing sizes of the particles with a given shape in the entire considered size range. As a result, for particles that are smaller than the critical value, the threshold field exceeds the breakdown value for air. It is found that for each given size of the particles there exists a minimum threshold field, such that the discharge from the particles with this (or smaller) size cannot be ignited in a lower-intensity field regardless of the particle shape. The dependences of the minimum threshold field and the corresponding degree of elongation of the particles on their longitudinal size are determined.

The direct writing and focusing of nanoparticles generated by an electrical discharge

Direct writing aims to deposit materials onto substrates in localised positions. In this paper, we demonstrate a new method for direct writing of nanoparticles at ambient-air-pressure. An electrical discharge is used to generate gold nanoparticles of the order of 10 nm diameter, which are then transported and 'focused' by an electric field in air, through the process of electric field-assisted diffusion, as opposed to normal ballistic focusing since the mean free path in air is very short. This process is novel and allows for practical normal atmospheric-pressure focused deposition of nanoparticles. The focusing mechanism is capable of producing patterned arrays of deposited nanoparticles with widths that are less than 10 % of the diameter of the focusing apparatus; in the present experimental configuration, gold spots with diameters of a few tens of micrometres were achieved, with ultimate size being limited by transverse diffusion and by charged particle mutual repulsion. In this study, the process of generating nanoparticles from bulk material, transporting and focusing these particles takes place in one operation, which is a key advantage in rapid prototyping and manufacturing techniques

Influence of the solid dielectric surface structure on the electric field at an air-barrier boundary

The distribution of electric field in air near a solid dielectric plate has been calculated using a model that takes into account the degree of roughness of the dielectric surface. Calculations performed for pyroceram show that the electric field strength at the vertices of juts on the dielectric surface can be 2.5IaeI3.5 times (depending on the degree of surface roughness) greater than the values in the air gap. At the same time, the field strength in hollows is about ten times weaker than that at the juts. The obtained results agree with experimentally observed [1] changes in the intensity of discharge processes at a dielectric surface with increasing degree of roughness.

Reactions of Organic Ions at Ambient Surfaces in a Solvent-Free Environment

Solvent-free ion/surface chemistry is studied at atmospheric pressure, specifically pyrylium cations, are reacted at ambient surfaces with organic amines to generate pyridinium ions. The dry reagent ions were generated by electrospraying a solution of the organic salt and passing the resulting electrosprayed droplets pneumatically through a heated metal drying tube. The dry ions were then passed through an electric field in air to separate the cations from anions and direct the cations onto a gold substrate coated with an amine. This nontraditional way of manipulating polyatomic ions has provided new chemical insights, for example, the surface reaction involving dry isolated 2,4,6-triphenylpyrylium cations and condensed solid-phase ethanolamine was found to produce the expected N-substituted pyridinium product ion via a pseudobase intermediate in a regiospecific fashion. In solution however, ethanolamine was observed to react through its N-centered and O-centered nucleophilic groups to generate two isomeric products via 2H-pyran intermediates. The O-centered nucleophile reacted less rapidly to give the minor product. The surface reaction product was characterized in situ by surface enhanced Raman spectroscopy, and ex situ using mass spectrometry and H/D exchange, and found to be chemically the same as the major pyridinium solution-phase reaction product.